Fluorescent light source



1947- L. R. BICKFORD, JR 2,413,940

FLUORESCENT LIGHT SOURCE Original Filed Jan. 1l 1944 H HM1 YJ=IHLATTORNEY Patented Jan. 7, 1947 FLUORESCENT Lron'r SOURCE Lawrence R.Bicktord, Jr., State College, Pa., as- I signor to Sylvania ElectricProducts Inc., Emporium, Pa., a corporation of Massachusetts Originalapplication January 11, 1944, Serial No. 517,806. Divided and thisapplication March 16, 1944, Serial No. 526,768

7 Claims.

. ing this result is to use a filter glass which absonbs the shortwaveultraviolet, while passing the long wave ultraviolet radiation. This maybe accomplished by making the envelope of the arc lamp of Corningultraviolet transmission glass #504 or #589 or by interposing a bluecorex glass filter-Corning filter glass #986 between a quartz mercurylamp and the object to be exposed to the. long wave ultravioletradiation.

This procedure has the disadvantage that the short wave ultravioletenergy produced by the light source is wasted, and is converted intoheat which may be undesirable.

This wasting of short wave ultraviolet energy has so far beenunavoidable in the conversion of ultraviolet radiation into visiblelight by fluorescent and phosphorescent materials which emit visiblelight in response to long wave ultraviolet radiation only, but have noexcitation band-1 in the short wave ultraviolet region which is'presentin most ultraviolet light sources.

It is, therefore, a principal object of the invention to producefluorescent light sources which emit long wave ultraviolet radiationviz., 3000 to 4000 A. in response to excitation by short waveultraviolet radiation, e. g., 2537 A.

It is another object of the invention to produce a fluorescent lampincorporating a cerium-activated phosphate glass.

It is a still further object of the invention to produce fluorescentlight sources embodying a filter; glass which passes long waveultraviolet and visible radiation, and absorbs short wave ultravioletwithout-transforming it intoheat.

According to another object of the invention, means are provided forincreasing the luminous eflicien cy of fluorescent lamps and the like.

Another principal object of the invention relates to an envelope for agas or vapor discharge lamp which consists of two layers of fluorescentglass, the inner layer being made of ceriumactivated phosphate glass;the outer of a material emitting visible light primarily in response tolongwave ultraviolet radiation.

An additional object of the invention is to provide a fluorescent lampwith a cerium-activated phosphate glass comprising one or several of thephosphates of elements of the first, second and third groups of theperiodic system.

According to a feature of the invention, means are provided including acerium-activated phosphate glass, to produce visiblefluorescence from asource of short wave ultraviolet radiation by multiple, frequencyconversion.

A further feature of the invention relates to a fluorescent lampembodying a metal phosphate glass having the optimum content oftrivalent cerium for producing improved conversion of short waveultraviolet into long wave ultraviolet radiation.

Another feature of the invention relates to a fluorescent lamp having acerium-activated phosphate glass consisting of the phosphates of A1-,Zn, and Ba in certain preferred proportions.

In the drawing which represents certain preferred embodiments,

Fig. 1 illustrates an experimental set-up to explain the invention.

Fig. 2 is a simplified diagram of an ultraviolet lamp and casingaccording to the invention.

Fig. 3 is a sectional view of Fig. 1 taken along the line 3-3 thereof.

Fig. 4-is a modification showing the invention 1 embodied in afluorescent lamp.

I the line 7-? thereof.

The cerium-activated phosphate glasses according to the invention may bemade up from diiferent types of raw materials. According to I onemethod, the raw batch comprises P205 and compounds in the form of saltsof elements of the first, second and third groups of the periodicsystem, which transform into the metal oxides during melting of the rawbatch. To the raw batch-is added up to 10% of a cerium salt (e. g.,C6203, CeOz, Ce(N03)4. Ce(N03)a and a reducing agent, such as AS203, redphosphorus, aluminum powder, or cream of tartar.

According to another method, the raw batch consists of one or a mixtureof several meta- ,phosphate's of the elements of the second and thirdgroups of the periodic system, c. g., Zn(PO3)2; BaCPOsh; A1(PO3)3. Tothis raw batch are added cerium salts and reducing agents as in thefirst method. Preferred mixing ratios of the three metaphosphates formaking my cerium-activated phosphate glasses are given in table.

able source S into long wave ultraviolet radiation.

An added amount of long wave ultraviolet radim 5 (4) 'ation, emitted byglass plate P, passes therefore through filter F, and increases thevisible light 50 o 25 5 mission of glass plate G in the region A as.com- B11008), 0 so 25 45 pared with that emitted on side B. (Pom m 50 5040 Taking advantage of this phenomenon, I have 1 built two types oflamps. The first type shown Cerium-activated phosphate glasses having inFigs. 2 and 3 consists of a combination of an similar proportions asthose made up from the ordinary black light" ultraviolet lamp I, (whichmetaphosphates, but made up of the raw maconsists of a mercury arc lampbuilt into a fixterials according to the first-mentioned method, turehaving an outer casing or window 3 made viz., starting from P205 andeither ZnO, BaO. 4 of red-purple Corex A" glass (or Corning A1203 or2Zn(COa).3Zn(OH)z or B8.(C0a) are, of #986) with a secondcerium-activated phoscourse, equivalent to the preferred glasses ac- 1phate glass plate or wall 2 interposed between cording to the table. theare lamp and the Corex A glass filter.

I have found that the addition of 2% to 4% This e J p delivers a eramount of long cerium to mixture (4) of table,'introduced prefywaveultraviolet radiation from any given are erably in the form of C8203 orof cemomerno, lamp t a the co ve c light amps.

with further addition of an appropriate amount and is therefore ofhigher eflicien y in the long of any of the above described reducingagents wave ultraviolet region than are the commercial yields a glasswith a relatively high conversion ps o this y Incidentally, e "C eX A"of shortwave ultraviolet radiation, e. g.,'2537 A. fi t r 3 i not as hotdu p at n, caus into long wave ultraviolet radiation between Of the factthat the short wave ultraviolet radi- 3000 and 4000 A v ation is notabsorbed and transformed into heat.

According to the invention, these new phos- 8.5 is the case with theconventional lambs. For

phate glasses are used as light filters and for a detailed disclosure ofa device such as lamp I, multiple frequency conversion equipment in newr f rence may be had to U. S. Patent No combinations with gas and vaporarc lamps in 2.383.189.

ma r ab t t b d scrib d, 7 A second type of lamp according to the inven-Fig. 1 shows in diagrammatic form, an ex-. @1011. as Shown in Figs- 4and nsist of ai perimental arrangement illustrating the.princi- Suitablepe 4 ich contains the usual ples of the invention. A plate of any glass(G) ure of gas and vapor fillin a c stom rily capable of emittingvisible fluorescence onexeiemployed in commercial fluorescent p tationby long waveultraviolet radiation (as are as Mounted at osite ends f theenvel pe. which t manganese activated phosphate qr Silicate ends are ofcourse sealed, there are the usual glasses) -is exposed to the radiationoriginally proelectrodes 5 and either both of ch may duced by anultraviolet source s from whi h the be of the thermionic or of thefield-emission type. short wave and visible radiation haslbeen'filteredIt Will be understood course; that the elecout by a Corex black filterF, made of a glass com- 40 trodes 5 and 6 are connected in'circuit withany merciauy kngwn as Coming 6 e well-known starting control arrangementsuch as purple Between the light sources is ordinarily employed incommercial fluorescent wh1ch maybe of weh known type, 'such f r lamps.In accordance with the present invenexample as Shown in 3. Patent2283189, tion, envelope 4 is made of a cerium-activated d the filter Fis placed a glass sheet p com phosphate glass as above described. Inaccordsisting of one of the new phosphate glasses ance with theinvention also, the exterior surcording to the invention, and coveringabout one face of envelope 15 Provided with a coating 7 half of the areaof Corex filter F, in the region of one of the well-known fluorescentmaterials marked A in the drawing In the right half which emit visiblelight more readily in response marked B in the drawing, the radiationfrom to long wave ultraviolet radiation than they do light source 5passes only the filter F before to short wave ultraviolet radiation.This coating striking, glass plate G i e" no phosphate glass 1 may forexample be of zinc sulfide. For a deis interposed between light source,S and filter F tailed disclosure of the construction of such a Thestriking phenomenon observed with this lamp to which the coating can beapplied arrangement is, that the glass plate G remains 65 erence ishereby made to Patent 21283" comparatively dark on th side marked 13while 189. the disclosure of which is incorporated hereit emits a largeamount of visible light on the in expressly since in the type of lampshown side marked A, where the phosphate glass P has in Figs. 4 and 5,the'actual fluorescent coating is been interposed between the source Sand the' applied externally of the envelope it 15 filter The result isstriking and unexpected sible to use for illumination purposes, sulfidesfor any one not familiar with the new fiuores- Such as 'zns; Zncds;These sulfides cent glass because the expected interpretation of be usedsuccessfully! this Particular the glass plate P would be that ofanadditional field the Past, because when they are applied filter, i. e.,of a partly transparent shield which as coating internally of theenvelope they absorbs part of the radiation from light source aredestroyed by the are Vapor discharge The usual observer would thereforeexpect H tween the electrodes 5 and 8. It will be underthat the visiblefluorescence of gla s plate on Stood 01' course, the invention is nOtthe side marked A could only be weaker or at to any particular kind offluorescent coating 1. best just as good, as on side If desired. otherfluorescent materials which The explanation of the fact t glass plateemit visible radiation preferably in response to G emits more visibleradiation on the side where 10118 Wave ultlfa-vifllell excitation ay bused a the phosphate glass P has been interposed bea er a t p e 01 u hmatetween the light source S and thefilter F is, of ,rials are organicfluorescent materials such as course, the property of my new glass toconvert the rhodamlnes, or U-activated CaFz, CaO, or the short waveultraviolet radiation of the light 76 z inc vanadate.

above-described auaeso In another embodiment of this type of fluorescentlamp, and as shown in Figs. 6 and I, the envelope may consist ofan-internal evacuated and sealed tube 8, carrying at opposite ends theusual electrodes 9 and ill, for sustaining an ultravioletproducing.discharge within the cavity of the tube 8 which cavity contains theusual fllling of metallic vapor such as mercury vapor and a smallpercentage of a gas such as argon, helium and the like as describediorexample in said U. 8. Patent No. 2,283,189. Surrounding the tube 8 andin spaced relation thereto, is another glass tube II. In accordance withthe invention, the envelope 8 is composed of one of the cerium-activatedphosphate glasses, while the outer casing ll consists ofmanganese-activated phosphate glass. When a gaseous discharge ismaintained between. the electrodes 9 and ill in the well-known manner,there is emitted both long and short wave ultraviolet radiation. Thelong wave radiation passes substantially freely through the wall ofmember a and excites the member II to visible fluoresence. At the sametime, ,the short wave radiation from the discharge is converted bymember I to long wave ultraviolet radiation which supplements theexcitationof the member ll, thus increasing the overall fluorescentefllciency oi the device. The flrst factor causing this increase ofefllciency is-the pre-converslon of short wave ultraviolet radiationinto long wave ultraviolet radiation by means of the member 8 asdescribed above. The second factor is the lowmeans to generateultraviolet radiation having long and short ultraviolet wavelengthcomponents, means mainly responsive to excitation only by long waveultraviolet to produce visible fluorescence, and means including acerium-activated phosphate glass located between said generator meansand said responsive means to convert said short wavelength componentsinto long wavelength components whereby visible light is produced inresponse both to said long wave components and to said short wavecomponents.

2. A fluorescent lamp comprising a sealed envelope containing anionizable medium for producing ultraviolet radiation including long andshort wave length components. the envelope being 01' a glass which hasthe property oi usefully converting a substantial. part of the shortwave components into long wave components, and

fluorescent means carried by said envelope and responsive to theoriginal long wave components and to said converted components toproduce visible fluorescence. I

3. A fluorescent lamp according to claim 2 in which the glass of theenvelope is of the ceriumactivated phosphate type.

4. A fluorescent lamp according to claim 2 in which said fluorescentmeans is in the form of a stratum on the exterior 01' said envelope.

ering'oi temperature of the visible fluorescent provides a greater heatradiating surface.

It will be understood of course that the invention is not limited to theparticular structures. shapes. or materials herein mentioned, but

that various changes and modifications may be made therein withoutdeparting from the spirit and scope of the invention.

This application is a -division of application Serial No. 517,806, fliedJanuary 11, 1944.

What is claimed is:

l. A fluorescent light source comprising.

5. A fluorescent lamp comprising a pair of spaced glass casings, one ofwhich has means to support on its interior a discharge for producingultraviolet radiations containing long and short wave lengths and beingoi. a glass which has the property 01 usefully converting shortultraviolet wave lengths into long ultraviolet wave lengths, andfluorescent means responsive to said long ultraviolet wave lengths andto said converted wave lengths and carried by the other or said casings.

6. A fluorescent lamp according to claim 5 in which the casings surroundeach other, the inner casing being of cerium-activated phosphate glass,-

and the outer glass casing being of manganeseactivated fluorescentglass.

'7. A fluorescent lamp comprising an enclosing.

glass envelope having means to produce an electric discharge therein,which discharge produces long wave length ultra-violet and a substantialportion of short wave length ultra-violet, a signal fluorescent coatingon the wall of said envelope and responsive substantially entirely tolong wave length ultra-violet; and means incorporated in said glass forconverting the short wave length ultra-violet from said discharge intolong wave length ultra-violet before acting on said fluorescent coating.

. LAWRENCE R. BICKFORD, Ja.

